The present invention relates in general to a method for affixing individual fibrils to a film, and in particular but not by way of limitation, to a method for affixing individual fibrils to a three-dimensional formed and apertured film by causing a low melt point web to intermingle with and/or captivate individual fibrils of essentially non-melting material, wherein the fibrils become partially embedded and/or entangled in the low melting point web to form a composite temporary web of both a low melt point polymer and the affixed fibrils, and subsequently introducing the composite temporary web into a second molten web of higher melt temperature, thereby causing the temporary web to melt into the contacting face of the second molten web and subsequently in preferred embodiments aperturing and forming the permanent film.
Absorbent articles such as sanitary napkins, incontinent devices, diapers, wound dressings and other products are well known. These articles absorb liquid and retain the liquid within a core. The interior or topsheet of the absorbent article is made of a flexible plastic film material. A negative characteristic of the flexible plastic film material is a glossy or xe2x80x9cplasticxe2x80x9d look and sticky tactile feel. It is desirable to produce absorbent devices which have a cloth-like look and feel to a user""s skin.
Many types of films have been proposed to overcome these tactile problems, such as the film disclosed in U.S. Pat. No. 4,995,930, which depicts a system for laminating a perforated plastic film and a fibrous web material, wherein a pneumatic vacuum is used to perforate the film when it is in a thermoplastic condition. However, the prior art relies on the existence of a web, and does not teach the application of individual fibrils that are not in a web structure. In commonly-owned U.S. application Ser. No. 08/850,635, the lack of a web is compensated for by the presence of a continuous belt, which carries a controlled amount of individual fibrils onto the molten web. The resulting web is subsequently formed and apertured with the composite component of the fibrils affixed to the contour of the user-side surface.
U.S. application Ser. No. 08/850,635 does not teach that fibrils are bound together to form a web, therefore the film disclosed therein lacks the integrity and transport properties of a web; hence, it is taught that they are conveyed by a belt. Further, because the conveying belt or drum of U.S. application Ser. No. 08/850,635 is cumbersome and difficult to maintain in the precise operating parameters required, inventive means must be incorporated to deliver the fibrils to the film-forming step in order to create the composite structure of a film with a fibrilized surface that follows the contour of the funnel-like cells, rendering them unobstructed.
The method of this invention eliminates the need for the carrier/conveyor belt by providing a composite temporary web with web integrity that can be transported directly into the lamination/forming process. Once the temporary web is in contact with the molten face of the film forming web, the temporary web melts and fuses, thereby depositing and embedding the fibrils thereto.
In the first embodiment, a flocking or metering device is provided for dispensing a controlled amount of individual fibrils. The fibrils are delivered onto a moving conveyor belt, which in certain embodiments may comprise a vacuum belt having a porous surface for drawing the layer of fibrils thereto. The unbonded fibrils are individual or substantially individual during dispersion from the flocking device, and remain unbonded after dispersion. Next, the fibril layer is transported and held by the vacuum conveyor belt to a position under a slot cast extrusion die, where a low temperature polymer melt is released. Upon release of the low temperature polymer melt, a vacuum pulls the low temperature polymer melt onto the surface of the fibril layer with a predetermined amount of pressure. This pressure may be sufficient to cause the fibrils to embed in the contacting surface of the polymer film, especially if tacky polymers are employed such as EVA, EMA, EEA, and others.
If low melt temperature polyethylenes are used, one can then deliver the combined polymer film and fibril layer to a nip point between a pair of nip rollers to cause sufficient pressure to captivate the fibrils and create the composite temporary web. Proximity positioning or very light pressure of the nip rollers is preferable to avoid flattening the fibrils onto the polymer film. In this manner, only a portion of most of the fibrils becomes embedded and affixed to the temporary polymer film. The more substantial portion of the fibrils maintain at least one loose end protruding off the surface of the composite temporary web.
These composite temporary webs may next be spooled or wound into master rolls for further processing at a later time, or processed in-line with subsequent process equipment to be combined with the higher temperature polymer melt under a second slot cast extrusion die for formation of the permanent film. This second in-line option will provide a continuous process mode as opposed to the roll option, which requires a secondary batch process. These options are available for all embodiments described herein.
During the combination with the higher temperature polymer melt, the lower melt temperature portion of the composite temporary web melts and fuses into the higher temperature polymer melt. The resulting permanent film is drawn against a perforated vacuum forming screen having a pressure differential to create funnel-like contours and apertures in the film and allow the fibrils to embed into and follow contours of the permanent film. A majority of aperture openings remain free of fibrils. It is also contemplated within the scope of this invention that these methods can apply to any known film making process. Smooth films and embossed films, as well as the preferred three-dimensional apertured films, can benefit by being enhanced with a surface of soft fibrils.
In a second embodiment, a flocking or metering device is provided to dispense the fibrils. From the device, the fibrils are delivered onto a moving vacuum belt having a porous surface for drawing and holding the fibrils thereto. The unbonded fibrils are individual or substantially individual during dispersion and remain unbonded after dispersion. Next, the fibril layer is transported and held by the vacuum conveyor belt to a position under a nonwoven meltblown extrusion die, which has a plurality of air slots releasing air streams at converging angles. The converging air streams create a turbulent zone for the dispersion of the lower temperature polymer melt, which is released from the extrusion die in fiber-like strands.
The layer of fibrils is next combined with the lower temperature polymer melt on a porous surface of a conveyor belt wheel having an internal vacuum which creates a vacuum zone to form a composite temporary web. While the fibrils are somewhat adhered to but mostly entangled in the lower temperature polymer melt web, the fibrils do not melt or bond by fusing. Nonetheless, the fibrils are captivated in the lower temperature polymer melt to form the composite temporary web.
In a third embodiment of the present invention, a flocking device for dispersing a controlled amount of fibrils is suspended adjacent to a nonwoven meltblown extrusion die. Gravity and venturi forces cause the controlled amount of fibrils dispersed over a controlled slot-like area, as determined by the exit slot of the flocking/metering device, to fall and be pulled into the path of converging air streams of the nonwoven meltblown process. Then, being caught in the converging air streams, the fibrils become somewhat adhered to and mostly entangled in and thus captivated during the forming of the lower temperature polymer melt as it is drawn down to the vacuum belt, which flattens and forms the lower temperature polymer melt. This process creates the composite temporary web.
To summarize, the first embodiment extrudes a molten polymer film on a surface of a layer of fibrils combined with a light pressure to embed a portion of the fibrils into the polymer film surface, thereby captivating the fibril layer. The second and third embodiments introduce fibrils into a nonwoven meltblown web at various stages of the formation of the temporary composite web. A meltblown process extrudes multiple strands of hot polymer into converging air streams that create a turbulent zone. The turbulence causes the strands to xe2x80x98dancexe2x80x99 and entangle as a vacuum belt pulls the strands to the belt surface. As the strands strike the vacuum belt, they remain in a molten state to thereby fuse and bond at the interstices of the randomly dispersed fibers.
The second embodiment introduces the layer of fibrils onto the vacuum belt such that the nonwoven meltblown web lands on top of the layer of fibrils and partially adheres to, but mostly entangles, the upper ends of the fibrils to captivate the fibrils.
The third embodiment introduces the fibrils into the turbulent air stream formed in the nonwoven meltblown process wherein the fibrils become entangled and captivated.
In all embodiments, the material with the highest melt point stability is the fibril, whose temperature parameters are controlled to maintain the fibril softness and integrity. The material with the lowest melt point stability is the polymer used to form the temporary web. The material of the permanent film has a melt point in between, such that the permanent film melts and fuses the temporary film or web onto its contacting surface, thereby leaving the fibrils deposited and embedded thereto with most of the fibrils maintaining at least one loose end.